1. Field of the Invention
The present invention relates to a method for etching a mercury cadmium tellurium substrate (hereinafter referred to as an HgCdTe substrate), and more specifically to a method for etching an HgCdTe substrate selectively by dry etching.
2. Description of the Prior Art
HgCdTe is promising as a material for a highly sensitive infrared detector element. Further, in order to improve resolution of an infrared detector element, it is required to form separation grooves in a substrate for separating pixels so that electrons excited in a specific pixel by infrared irradiation do not pass into an adjacent pixel. For forming those separation grooves, it is demanded to establish etching technique of an HgCdTe substrate.
In dry etching of an HgCdTe substrate, mixed gas of Ar+H.sub.2 or mixed gas of H.sub.2 +CH.sub.4 has been heretofore used (reference documents: Appl. Phys. Lett., No. 59, p1752 (1991)).
In the etching using a mixed gas and a resist film 2a as a mask as shown in FIG. 1, however, it happens sometimes that the resist film 2a is etched during etching of an HgCdTe substrate 1a due to low selectivity of the HgCdTe substrate 1a versus the resist film 2a, and the substrate 1a to be protected is exposed and etched when forming the separation groove 5.
Further, the resist film 2a changes in quality and solidifies by irradiation with plasma of the mixed gas, and removal by an organic solvent becomes difficult. As a result, the resist is left on the surface of the substrate 1a, which makes processing thereafter difficult.
In order to avoid such a status, there is a method of using as an etching mask a two-layer film composed of an aluminum film 3 and a resist film 2b as shown in FIG. 2 to obtain a separation groove 5b. Further an insulating film such as a SiN film 4 as an etching mask as shown in FIG. 3 (Described in Japanese unexamined publication (Kokai) Hei 4-073733) to obtain a separation groove 5c is employed.
However, a forming process for the aluminum film 3 and the insulating film 4, and in addition, a patterning process for these films or the like are required for forming such an etching mask. Hence, simplification of the process cannot be achieved.
Further, although change in quality and solidification of the resist mask are avoidable in the case that the resist film as a mask is used in sputter etching using Ar gas (reference documents: Journal of Crystal Growth 73 (1985) 379-384) in order to simplify the process, there arises a risk of causing damage on the substrate. When the substrate is damaged, a leak current passes through a PN junction. Hence, the sensitivity of the infrared detector element may be lowered, or a pixel separation may become insufficient.